1. Field of the Invention This invention relates to propulsion arrangements for wheeled vehicles.
The present-day motor car is inefficient mainly because it has to operate over a wide range of speeds using a single engine. Its use for long journeys at high speeds may decline somewhat with improved inter-city public transport and with increasing cost of gasoline, but its use for short door-to-door journeys, for which it is very convenient, will undoubtedly continue. These short journeys will also remain the main reason for the car's inefficiency, unless a way is found of circumventing the inefficiency of the internal combustion engine when it is operating at less than about one-tenth of its maximum power (e.g. supplying power to propel a car at less than 35 m.p.h. when it is capable of propelling the car at 85 m.p.h). This inefficiency arises mainly from the mechanical losses in the engine, which losses are largely independent of output torque and amount to 20-25% of maximum torque. They cannot be made insignificantly small by reducing the speed of the engine because of its limited range of efficient operation. The car's efficiency is further reduced by its fuel consumption during retardation (using the brakes or engine braking), during idling in traffic and during rapid opening of the throttle for high acceleration.
A potentially attractive way of reducing fuel consumption is to use for a wheeled vehicle a propulsion arrangement of a character comprising a prime mover constituting a source of power for propelling the vehicle and an inertial energy store, separate from the prime mover, which can be charged with mechanical energy and can also serve for propelling the vehicle.
The prime mover of a propulsion arrangement of the above character can be, for instance, a gasoline- or diesel-fuelled internal combustion engine, or an electric motor which is energised from a battery carried on the vehicle. The inertial energy store is suitably a fixed mass flywheel. Hereinafter, for the sake of convenience, the word "engine" is used to denote any form of prime mover and the word "flywheel" is used to denote any form of inertial energy store.
2. Description of the Prior Art
Propulsion arrangements of the above character are already known and, in general, include coupling means by which a vehicle drive shaft can be connected through suitable gearing to the engine alone, to the flywheel alone, or to the engine and the flywheel together. The coupling means also connect the engine to the flywheel, so that within the propulsion arrangement there can be flow of mechanical power in either direction between any pair of the three inter-connectable elements (engine, flywheel and vehicle drive shaft) of the arrangement. However, it is believed that hitherto these six available directions of mechanical power flow have not been used to the best advantage.
A known method of operation of the propulsion arrangement is to use selectively energy stored in the flywheel to provide power only to supplement, and not to replace, power produced by the engine in propelling the vehicle, for instance during periods of acceleration of the vehicle, while power from both the vehicle and the engine is used to store energy in the flywheel at other selected times, for instance during retardation or braking of the vehicle and during periods when there is excess power available from the engine above that required to maintain the vehicle in a prevailing running condition. With this method of operation, the flywheel is likely, at a journey's end, to be storing useful energy which will be wasted. Also, other work done to date on these propulsion arrangements having an assisting flywheel has been largely of a mechanical nature, focussing on the construction of high energy-density flywheels (which aggravate the energy waste at the end of a journey in the above method of operation), and on the consequent problems of recucing high windage losses, of overcoming gyroscopic effects, of increasing bearing life and of overcoming safety hazards, for instance by containment, in the event of a burst flywheel. The main reasons for wanting a high energy-density flywheel are that more auxiliary power is available to increase maximum vehicle acceleration, particularly on up-gradients, the period for which the auxiliary power can be sustained is longer, and more energy can be stored in the flywheel during regenerative braking, particularly on down-gradients.